“Under The Banner of Heaven” wants to be both a thrilling true crime drama and a faith-shaking takedown of the religious right. But so far, its treatment of the topic is too shallow and too un-self-aware to challenge anyone who doesn’t already agree with it. The seven-part FX series is an adaptation by Dustin Lance Black of Jon Krakauer’s true crime bestseller about a murder in a “fundamentalist” community of Latter-day Saints, commonly known as Mormons.